The Pioneer plaques are a pair of gold-anodized aluminium plaques which were placed on board the 1972 Pioneer 10 and 1973 Pioneer 11 spacecraft, featuring a pictorial message, in case either Pioneer 10 or 11 is intercepted by extraterrestrial life. The plaques show the nude figures of a human male and female along with several symbols that are designed to provide information about the origin of the spacecraft.
The Pioneer 10 and 11 spacecrafts were the first human-built objects to achieve escape velocity from the Solar System. The plaques were attached to the spacecraft's antenna support struts in a position that would shield them from erosion by stellar dust.
- 1 History
- 2 Physical properties
- 3 Symbolism
- 4 Criticism
- 5 In popular culture
- 6 See also
- 7 References
- 8 External links
The original idea, that the Pioneer spacecraft should carry a message from mankind, was first mentioned by Eric Burgess when he visited the Jet Propulsion Laboratory in Pasadena, California, during the Mariner 9 mission. He approached Carl Sagan, who had lectured about communication with extraterrestrial intelligences at a conference in Crimea.
Sagan was enthusiastic about the idea of sending a message with the Pioneer spacecraft. NASA agreed to the plan and gave him three weeks to prepare a message. Together with Frank Drake he designed the plaque, and the artwork was prepared by Sagan's then-wife Linda Salzman Sagan.
Both plaques were manufactured at Precision Engravers, San Carlos, California.
The first plaque was launched with Pioneer 10 on March 2, 1972, and the second followed with Pioneer 11 on April 5, 1973.
- Material: 6061 T6 gold-anodized aluminum
- Width: 229 mm (9 inches)
- Height: 152 mm (6 inches)
- Thickness: 1.27 mm (0.05 inch)
- Mean depth of engraving: 0.381 millimeters (381 µm) (0.015 inch)
- Mass: approx. 0.120 kilograms (120 g) (4.2 oz)
Hyperfine transition of neutral hydrogen
At the top left of the plate is a schematic representation of the hyperfine transition of hydrogen, which is the most abundant element in the universe. Below this symbol is a small vertical line to represent the binary digit 1. This spin-flip transition of a hydrogen atom from electron state spin up to electron state spin down can specify a unit of length (wavelength, 21 cm) as well as a unit of time (frequency, 1420 MHz). Both units are used as measurements in the other symbols.
Figures of a man and a woman
On the right side of the plaque, a man and a woman are shown in front of the spacecraft. Between the brackets that indicate the height of the woman, the binary representation of the number 8 can be seen (1000, with a small defect in the first zero). In units of the wavelength of the hyperfine transition of hydrogen this means 8 × 21 cm = 168 cm.
Originally Sagan intended for the humans holding hands, but soon realized that an extraterrestrial might perceive the figure as a single creature rather than two organisms. One can see that the woman's genitals are not really depicted; only the Mons pubis is shown. It has been claimed that Sagan, having little time to complete the plaque, suspected that NASA would have rejected a more intricate drawing and therefore made a compromise just to be safe. However, according to Mark Wolverton's more detailed account, the original design included a "short line indicating the woman's vulva". It was erased as condition for approval by John Naugle, former head of NASA's Office of Space Science and the agency's former chief scientist. 
Sagan himself, however, later wrote:
"The decision to omit a very short line in this diagram was made partly because conventional representation in Greek statuary omits it. But there was another reason: Our desire to see the message successfully launched on Pioneer 10. In retrospect, we may have judged NASA's scientific-political hierarchy as more puritanical than it is. In the many discussions that I held with such officials up to the Administrator of the National Aeronautics and Space Administration and the President's Science Adviser, not one Victorian demurrer was ever voiced; and a great deal of helpful encouragement was given… The idea of government censorship of the Pioneer 10 plaque is now so well documented and firmly entrenched that no statement from the designers of the plaque to the contrary can play any role in influencing the prevailing opinion. But we can at least try."
Relative position of the Sun to the center of the Galaxy and 14 pulsars
The radial pattern on the left of the plaque shows 15 lines emanating from the same origin. Fourteen of the lines have corresponding long binary numbers, which stand for the periods of pulsars, using the hydrogen spin-flip transition frequency as the unit. Since these periods will change over time, the epoch of the launch can be calculated from these values.
If the plaque is found, only some of the pulsars may be visible from the location of its discovery. Showing the location with as many as 14 pulsars provides redundancy so that the location of the origin can be triangulated even if only some of the pulsars are recognized.
The data for one of the pulsars is misleading. When the plaque was designed, the frequency of pulsar "1240" (now known as J1243-6423) was known to only three significant decimal digits: 0.388 second. The map lists the period of this pulsar in binary to much greater precision: 100000110110010110001001111000. Rounding this off at about 10 significant bits (100000110100000000000000000000) would have provided a hint of this uncertainty. This pulsar is represented by the long line pointing down and to the right.
The fifteenth line on the plaque extends to the far right, behind the human figures. This line indicates the sun's relative distance to the center of the galaxy.
The pulsar map and hydrogen atom diagram are shared in common with the Voyager Golden Record.
At the bottom of the plaque is a schematic diagram of the Solar System. A small picture of the spacecraft is shown, and the trajectory shows its way past Jupiter and out of the solar system. Both Pioneers 10 and 11 have identical plaques; however, after launch, Pioneer 11 was redirected towards Saturn and from there it exited the Solar System. In this regard the Pioneer 11 plaque is somewhat inaccurate. The Saturn flyby of Pioneer 11 would also greatly influence its future direction and destination as compared to Pioneer 10, but this fact is not depicted in the plaques.
Saturn's rings could give a further hint to identifying the Solar System. Rings around the planets Jupiter, Uranus and Neptune were unknown when the plaque was designed; however, unlike Saturn the ring systems on these planets are not as easily visible and apparent as Saturn's. Pluto was considered to be a planet when the plaque was designed; in 2006 the IAU reclassified Pluto as a dwarf planet and then in 2008 as a plutoid. Other large bodies classed as dwarf planets, such as Sedna, are not depicted, as they were unknown at the time the plaque was made.
Silhouette of the spacecraft
One of the parts of the diagram that is among the easiest for humans to understand may be among the hardest for the extraterrestrial finders to understand: the arrow showing the trajectory of Pioneer. An article in Scientific American criticized the use of an arrow because arrows are an artifact of hunter-gatherer societies like those on Earth; finders with a different cultural heritage may find the arrow symbol meaningless.
In popular culture
- In the science fiction film Star Trek V: The Final Frontier, the plaque is shown attached to a Pioneer probe floating in space—just before the probe is intercepted and destroyed by a bored Klingon ship captain, who scoffs "Shooting space garbage is no test of a warrior's mettle." However the plaque is erroneously depicted as facing outwards rather than inwards.
- In the Star Trek novel Federation, a character mentions that humans had shown copies of the plaque to several alien races they encountered, but none had been able to decode it.
- In "The Message," an episode of the science fiction series The Outer Limits, a deaf woman was featured receiving alien signals through her cochlear implant, prompting her to write out Xs, 1s, and 0s on paper. When put together, the Xs turned into the images of the man and woman from the plaque, along with an extraterrestrial humanoid raising a hand in a peaceful gesture.
- On her album United States Live, American performance artist Laurie Anderson contemplates extraterrestrials finding the plaque and asks "do you think that they will think his arm is permanently attached in this position?"
- In an episode of Futurama called "Godfellas," the robot Bender finds himself doomed to drift through space, during which time he etches a modified version of the Pioneer plaque, with himself towering menacingly over the human figures, so that "When I'm found in a million years, people will know what the score was."
- In Buck Rogers season 1, episode 15 "Ardala Returns," Princess Ardala constructs a fake probe (allegedly launched in 1996) that utilizes a copy of the plaque in order to trick Buck into thinking the probe was from his own time period — the distant past.
- In the L. Ron Hubbard novel Battlefield Earth, it is mentioned by the principal alien character that his race's conquest of Earth was made possible by their discovery of a space probe "that gave full directions to the place, had pictures of man on it and everything".
- In the April 15th 2012 episode of The Simpsons, the plaque was briefly shown at the end of the episode. It was depicted with an extraterrestrial holding the plaque upside down obviously confused with its strange depictions.
- The plaque is used as the artwork for the album Aufheben by The Brian Jonestown Massacre and for Accept the Signal by Regular Fries.
- A drawing which bears a strong likeness to the one depicted in the plaque was used as the artwork for Norwegian avant-garde metal band Arcturus' album Sideshow Symphonies.
- Alien language
- Communication with extraterrestrial intelligence
- Pioneer program
- Voyager Golden Record
- Arecibo message
- Carl Sagan, Linda Salzman Sagan and Frank Drake (1972-02-25). "A Message from Earth". Science 175 (4024): 881–884. Bibcode:1972Sci...175..881S. doi:10.1126/science.175.4024.881. PMID 17781060. Paper on the background of the plaque. Pages available online: 1, 2, 3, 4.
- Alan Fletcher, "The art of looking sideways", Phaidon Press, 2001. ISBN 0-7148-3449-1.
- Mark Wolverton, The Depths of Space: The Story of the Pioneer Planetary Probes, Joseph Henry Press, 2004, p. 79. ISBN 0-309-09050-4.
- Wolverton, supra, p. 80.
- Carl Sagan, Cosmic Connection: An Extraterrestrial Perspective, Cambridge University Press, 2000, ISBN 0-521-78303-8, pages 22-25
- Ernst Gombrich ‘The Visual Image’, 1972 in Scientific American (eds [clarification needed]) Communication. San Francisco, California, Freeman, pp. 46–60; originally in a special issue of Scientific American, September 1972; republished in Gombrich (1982) The Image and the Eye: Further Studies in the Psychology of Pictorial Representation, London, Phaidon, pp. 137–61.
- Cited in Carl Sagan, Murmurs of Earth, 1978, New York, ISBN 0-679-74444-4
|Wikimedia Commons has media related to Pioneer plaque.|
- NASA on the plaque
- NASA on Pioneer 10 & 11
- Reading the Pioneer/Voyager Pulsar Map (Wm. Robert Johnston), updated 11 March 2003. Last accessed on 8 April 2006
- Edward Tufte, Pioneer Space Plaque Redesign. A humorous critique of the plaque's design
- Precision Engravers are the company that manufactured the original plaques and still hold the master diagram.